It should be noted that US and UK practice is to express the sugar levels in different units. The commonly used US unit is mg/dL (milligrams per deciliter) and in those units the common guideline is that fasting level should be at 100 or below. A fasting level of 140 was, a few years back, the usual level at which many doctors recommended serious efforts to get lower, but recommendations regarding the level at which treatment should be begun has been decreasing and most docs would now suggest diet changes, weight loss, and often one of the milder "facilitator" drugs like metformin for fasting levels above 120.

The glucometers commonly used in the US rarely will "register" levels above about 450 or 500, and readings this high probably are not really accurate.

At the other end, most US glucometers will not register, and/or are inaccurate below about 40 or so. Most people are unconscious, or nearly so, at levels below about 45, but especially in Type I diabetics, and in Type IIs using insulin, some may become "acclimated" to transient lower levels and may see lower numbers.

Anything below about 50 probably requires immediate action to bring the level back up, and until individual tolerance is known professional - emergency - assistance may be needed.

One person of my acquaintance can usually "self treat" at levels as low as 40, but may need assistance at 36. About 35 or below is when we call "911" if there isn't an IMMEDIATE response. This is a person with unstable control and acclimated to episodes of very low glucose levels, and "normal diabetics" might go to the morgue rather than to the hospital at these levels.

For Type II, US doctors rely mostly on the "average" shown by lab tests, but again different units are generally used and the critical value is called the "A1C" level. It's listed on lab reports as a "%" but the reports don't say what's measured. Values between 4.7 to 6.4 are listed as "good" or "normal."

For fasting glucose levels, a range of 70 to 100 mg/dL is shown on the reports as "normal." Most physicians seem not to be too concerned if non-fasting levels are around 180 - 200 in Type II patients with otherwise good control, but at the high end (or above) some might suggest a brief period of readings over time following a meal to see whether the level declines normally.

Note that these comments are based on a dozen years of consultation with "pretty good" medical advisors to our family. They might help someone know what to discuss, and what questions to ask of their own medical consultants; but should not be considered "authoritative" by anyone.

John